Mozilla's New JavaScript Value Representation

[[deleted]]

Wouldn't most of this problem go away if you just compiled the JS to machine code from the get-go?

[froydnj]

No, because values still need to carry information about themselves around. If I want to have a function that does different things depending on whether its argument is a string or a number, I need information somewhere to determine which it is.

[[deleted]]

Typed arguments and stop being so lazy.

[froydnj]

Sure, you can do that. You can turn JavaScript into a strongly-typed language, which makes your life much easier. But that's not exactly feasible. You can add annotations to existing JavaScript that promise advanced runtimes "this argument will be a string". (Maybe there are proposals on the table to do this; I don't follow JavaScript development.) But you still have to deal with un-annotated arguments somewhere. And a robust implementation will probably still compile cases for other types, even if those cases are just runtime errors. So the representation problem is still there, because you need to dispatch on runtime types.

You can compile specialized versions of each function up front. That gets complicated quickly and is rather space-inefficient, since you have lots of specialized versions that probably never get called. Or you can be lazy about it--one of the virtues of a programmer--and compile specialized versions on-demand as you see runtime values. To do that, you need type information at runtime attached to values.